1. Field of the Invention
The present invention relates to the pixel structure and the terminal structure of an organic EL display device, and more particularly to the pixel structure and the terminal structure of an organic EL display device of top-emission-type.
2. Description of Related Art
Although a main stream of the conventional display device is a CRT, a liquid crystal display device, a plasma display device and the like which are flat display devices have been practically used in place of the CRT and a demand for such flat display devices is increasing. In addition to these display devices, developments and efforts for practical use of a display device which uses organic electro luminescence (hereinafter, referred to as organic EL display device) and a display device which arranges electron sources utilizing field emission in a matrix array and phosphors arranged on an anode is radiated with light thus forming an image (hereinafter referred to as FED display device) have been also in progress.
The organic EL display device has features such as (1) the organic EL display device is of a self-luminous type compared with liquid crystal and hence, a backlight is unnecessary, (2) power source necessary for emission of light is low, that is, equal to or below 10V and hence, the power consumption can be decreased, (3) compared to the plasma display device or the FED display device, the vacuum structure is unnecessary thus the organic EL display device is suitable for achieving the reduction of weight and the reduction of thickness, (4) a response time is short, that is, several micro seconds and hence, the organic EL display device exhibits the excellent motion picture property, and (5) the viewing angle is 170 degrees or more.
FIG. 11 is a cross-sectional view of the pixel structure of a so-called bottom-emission-type organic EL display device which has been developed conventionally. FIG. 11 is a cross-sectional view of a pixel portion of the display device which drives organic EL using a thin film transistor (TFT) as a switching element. In FIG. 11, an undercoat 2 is applied to an upper surface of a glass substrate 1. The undercoat 2 plays a role of preventing impurities from a glass substrate from contaminating TFTs and the organic EL. A semiconductor layer 3 is formed of a source portion, a channel portion and a drain portion. A gate insulation film 4 is formed to cover the semiconductor layer 3, a gate electrode 5 is formed on the gate insulation film 4, and an interlayer insulation film 6 is formed to cover the gate electrode 5. While an SD line 7 is formed on the interlayer insulation film 6, the SD line 7 is connected with the source portion or the drain portion formed on the semiconductor layer 3 via a through hole formed in the interlayer insulation film 6 thus playing a role to take out a signal from the TFT. A passivation film 8 is formed to cover the SD line 7 thus protecting the whole TFT.
While a transparent electrode (ITO) 12 which constitutes a lower electrode of an organic EL layer is formed on the passivation film 8, the transparent electrode 12 is connected with the SD line 7 via a through hole formed in the passivation film 8. Further, on the transparent electrode 12 and the passivation film 8, a bank 11 for removing each pixel is formed. On a portion of the transparent electrode 12 where the bank 11 is not formed, an organic EL layer 9 which constitutes a light emitting portion is stacked. Then, a metal layer 10 which constitutes an upper electrode is formed on the organic EL layer 9. The organic EL layer 9 is generally formed of a plurality of layers and emits light when a voltage is applied between a cathode and an anode. Here, the lower electrode is formed of a transparent electrode, and all of the passivation film 8, the interlayer insulation film 6 and the undercoat 2 are transparent and hence, light emitted from the organic EL layer 9 advances in the direction indicated by an arrow L in FIG. 12 (bottom emission). On the other hand, light which advances toward the upper electrode 10 is reflected on metal 10 which constitutes an upper electrode and is also advances in the direction indicated by an arrow L in FIG. 11.
The bottom-emission-type organic EL display device has following drawbacks. That is, a light emission effective region is limited due to the relationship with a switching element such as a TFT. Light from the EL may influence an operation of the TFT which is the switching element. Light from the EL has to pass through many layers such as the passivation film 8, the interlayer insulation film 6, the undercoat 2, the glass substrate 1 and the like and hence, a light takeout efficiency is lowered due to absorption of light in respective layers, the reflection of light between respective layers and the like.
Although the top-emission-type organic EL display device can overcome some of drawbacks attributed to the above-mentioned bottom-emission-type organic EL display device, the structure is still complicated and hence, the organic EL display device still suffers from drawbacks such as a high manufacturing cost and the insufficient reliability.
Here, patent document 1 describes the pixel structure of an organic EL display device which has the structure similar to the above-mentioned structure and is applicable to the top-emission-type structure. Further, patent document 2 describes the constitution which uses a layer substantially equal to the SD line as an anode of an organic EL layer.
[Patent Document 1] JP-A-2001-56650
[Patent Document 2] JP-A-2003-234188